1. Field of the Invention
The present invention relates to a resin encapsulation type semiconductor device, and more particularly to a resin encapsulation type semiconductor device used in a high frequency field.
2. Description of the Related Art
FIG. 10 is a cross sectional view of a conventional resin encapsulation type semiconductor device. As shown in FIG. 10, a semiconductor element 1 is mounted on a semiconductor mount 2. The semiconductor element 1 is electrically connected to lead portions 3 by wires 7. The semiconductor element 1, the semiconductor mount 2, the wires 7 and a part of each lead portion 3 are encapsulated with a resin portion 6.
FIG. 11 is a plan view of the lead frame of the resin encapsulation type semiconductor device shown in FIG. 10. It will be described how to manufacture the resin encapsulation type semiconductor device with reference to FIG. 11. In the first step, a rectangular thin metal plate is punched or etched to form a lead frame 9 comprising the semiconductor mount 2, the lead portions 3' and tie bars 8. Then, the semiconductor element 1 is mounted on the semiconductor mount 2 and joined to the lead portions 3 by the wires 7. Further, the semiconductor element 1, the semiconductor mount 2, and that region of each lead portion 3 which is positioned inward of the corresponding tie bar 8, i.e., on the side of the semiconductor element 1 are encapsulated with resin, with the other region of the lead portion 3, which is positioned outward of the tie bar 8, being exposed to the outside. Under this condition, the tie bars 8 for joining adjacent lead portions 3 each other are cut away, and then the lead portions 3 are bent. As a result, the end portion of the lead portion 3 away from the semiconductor element 1 is shaped as shown in FIG. 10.
In operating the semiconductor element included in the resin encapsulation type semiconductor device of the construction described above, it is necessary in some cases to apply a high frequency of at least several hundred kHz to the semiconductor element. In this case, the leads 3 connected to the power source terminals of the semiconductor element and the leads connected to the terminals of the signal system are alternately arranged in order to suppress signal reflection or noise generation.
In the conventional arrangement described above, however, the number of leads required is about twice as large as the number of kinds of the signals, making it necessary to enlarge the planar area on which these leads are arranged. Where the planar area on which the leads are arranged is enlarged while maintaining a predetermined distance between adjacent leads and a predetermined thickness of the lead, it is necessary to increase the length of the respective lead. If the length of the lead is increased, the transmission delay time within the package is increased. Also, the unevenness in the lead length and the edge surface in the processing tends to make it impossible to obtain an optimum value (50 .OMEGA.) of the characteristic impedance for suppressing the signal reflection. On the other hand, if the distance between adjacent leads connected to the power source terminal is decreased, the inductance component is enlarged so as to bring about fluctuation in current.